ANDRITZ ACB torrefaction

ACB is a brandname of the Austrian ACB consortium. The consortium was established in 2007 and consists of the technology company ANDRITZ AG, the Austrian based biomass-combustion technology supplier Polytechnik Luft- und Feuerungstechnik GmbH, and the consultancy company Wild und Partner of Vienna. The exclusive rights for commercialization of the know-how gained are held by ANDRITZ AG, represented by the SEPARATION business area in Graz, Austria.

The target of the ACB process development has been defined as developing a highly efficient, but simple way of producing torrefied fuel out of a broad range of possible biomass feedstocks. Process robustness and flexibility, as well as safety of operation are to be achieved using known and established components.

The commercial single-line production unit capacity has been defined at 50,000 t/a, and this production unit will focus on decentralized production concepts - production will take place at the biomass source.

The turnkey production unit contains all necessary process steps for producing densified, torrefied fuel, including waste gas utilization and thermal energy production, resulting in an independently operating fuel production unit - the ACB plant. The ACB plant can also be extended to produce electricity, which could be of interest under certain conditions, such as areas with low-level infrastructure.

Main process steps of the ACB plant

Biomass drying

Biomass is dried using the ANDRITZ BDS drying technology. In this case, a closed-loop, directly fired system is used, which has low thermal energy consumption, providing best preconditions for optimum overall efficiency.

Torrefaction

The ACB technology uses an indirectly heated, rotating drum reactor for the torrefaction stage. This technology provides high flexibility in terms of processable particle size as the particles do not need to be fluidized or to form a fixed bed. The mechanical design and the manufacturing expertise of the drum is based on experience with the ANDRITZ DDS (drum drying system), which is operating successfully in more than 100 drying lines worldwide.

Energy supply and lean gas utilization

Energy to heat the torrefaction drum and the belt dryer is supplied by a polytechnic biomass grate furnace. The furnace co-incinerates the lean gas from the torrefaction process.

Densification

The torrefaction process has shown significant effect on pelletizing properties. Research, tests, and pelletizing equipment configuration changes are ongoing to develop a feasible industrial pelletizing solution for torrefied wood. Parallel to optimizing the pelletization step, the ACB consortium is investigating opportunities for alternative densification technology, such as briquetting.

The ACB consortium erected a 1 t/h demonstration plant in Frohnleiten/Austria, with official start-up in October 2012.